1. Field of the Invention
The present invention relates to an apparatus for recording and reproducing video signals, or a video tape recorder (VTR), and more particularly, to an apparatus which can record and reproduce both of the MUSE (Multiple Sub-Nyquist Sampling Encoding) signals employed mainly for satellite broadcasting and the baseband signals frequently employed for studio use, video theater or as input signals from a video camera.
2. Description of the Related Art
Recently, a demand for high resolution television image has been rapidly increasing. To satisfy the demand, a so-called HD-TV (High-Definition Television) and satelite broadcasting employing signals with broader bandwidth than that of a conventional system are in a practical phase.
The baseband signals employed in the HD-TV system have a signal bandwidth more than 20 MHz to obtain high-definition image. Compared to bandwidths of current NTSC signals (4.2 MHz) and PAL signals (5.5 MHz), this bandwidth is about 4-5 times broader. Note that all the values above-mentioned are of luminance signals.
To record/reproduce the video signal with such broad bandwidth, it is required that the relative speed in scanning of a magnetic tape by a magnetic head and the rotation speed of a rotary drum holding the magnetic head are considerably increased.
For example, in a current VTR, the relative speed of a magnetic head and a magnetic tape is 5.767 m/s in the VHS system, and 6.993 m/s in the .beta. system. The rotation speed of a current rotary drum is 1800 r.p.m. Meanwhile, to record the baseband signals on a magnetic tape, the relative speed of the magnetic head and the magnetic tape have to be increased to two to four times greater than the current one, and the rotation speed of the drum is required to be increased to two to four times, i.e., 3,600-7200 r.p.m. Furthermore, to reduce the recording bandwidth, one track on a recording medium is divided into two channels to reduce the bandwidth per channel by half.
For example, in the case where a bandwidth of a baseband signal is 24 MHz, by dividing a track into two channels, the bandwidth per channel can be reduced to 12 MHz.
The MUSE signal is a signal transmission system developed for broadcasting high resolution image in the satellite broadcasting having limitation of available bandwidth. Accordingly, in transmission by the MUSE signal, the baseband signal is bandwidth-compressed to 8.1 MHz. Roughly speaking, the signal bandwidth required for recording/reproducing the MUSE signal can be less than half the signal bandwidth for processing the baseband signal.
An example of a VTR for recording baseband signals in the HD-TV system is disclosed by Masami Itoga et al in "Wideband Recording Technology for High-Definition Baseband VCRs" (1988. IEEE Vol. CE-33, No. 3, pp. 203-209).
One example of a VTR for recording the MUSE signal is as follows. The bandwidth of the MUSE signal is about two times wider than that in a conventional NTSC system. In a proposed VTR, the rotation speed of a rotatory drum is twice that of a conventional household VTR. One field period of video signal is divided into two segments and recorded on a magnetic tape in one channel. A VTR according to this system can record/reproduce signals over a longer time period than one specialized in the baseband signal.
As described above, the signal bandwidths of the baseband signal and the MUSE signal are considerably different from each other. Therefore, conventionally, apparatuses specialized in recording the baseband signal and apparatuses specialized in recording the MUSE signal have been separately manufactured.
However, as the satellite broadcasting and video theater having high resolution image employing the baseband signal are increasingly spreading, a demand for a VTR for utilizing them at home increases. Providing both apparatuses specialized in the baseband signal and the MUSE signal costs too much for use at home. Also, the space used by the apparatuses for processing respective signals should be saved.